Выполните действия: (4a+5b: 4a-5b-4a-5b: 4a+5b): (4a+5b: 4a-5b-1)

1)(4a+5b)/(4a-5b)-(4a-5b)/(4a+5b)=
=(16a²+40ab+25b²-16a²+40ab-25b²)/(4a+5b)(4a-5b)=80ab/(4a+5b)(4a-5b)
2)(4a+5b)/(4a-5b)-1=(4a+5b-4a+5b)/(4a-5b)=10b/(4a-5b)
3)80ab/(4a+5b)(4a-5b)*(4a-5b)/10b=8a/(4a+5b)